Feeling pressure from discount carriers, Alaska Airlines announced major upgrades Thursday to its flight schedule at San Francisco International Airport, and said it is matching the low fares of its competitors.

The Seattle-based airline said it is increasing its service to eight daily flights from SFO to Seattle, up from an average of six to eight. Alaska is moving quickly to match the fares of Burlingame-based Virgin America, which Tuesday will begin flying three times a day to Seattle from SFO.

Alaska said it will match the Virgin America one-way fare of $73. The eight daily SFO-Seattle flights will depart every two hours, starting at 7:30 a.m. The flight schedule changes will take effect April 27, but the competitively priced tickets are available immediately.

In addition, the airline will double mileage on its frequent-flier program for the rest of the year for passengers who fly Alaska twice through May 15.

“California is an important market for us, and we’re preparing to compete vigorously at SFO,” said Steve Jarvis, vice president of marketing and sales for the airline.

Alaska is pushing to lure more business travelers with the schedule convenience and low fares, Jarvis said. The airline is also including a hot breakfast on some morning flights.

Alaska also competes against Southwest Airlines and Virgin America in the lucrative SFO-Los Angeles route. It is offering a $38 one-way fare to Los Angeles International Airport.

“Alaska doesn’t have a choice,” said Michael Roach, principal at Roach & Sbarra, an airline consulting group in San Francisco. “Customers care more about prices than anything else except schedule.”

In a soft economy, and with Virgin America entering the market, Alaska has to match the fare or lose customers, Roach said. Virgin America launched its service at SFO in August.

Jarvis said the airline is being hit hard by this week’s rise in oil prices to $109 a barrel, but added that Alaska will defend its routes in California where there are fare wars.

Alaska and its regional airline, Horizon Air, average a total of 44 daily flights from SFO. Other destinations for the airlines include Portland; Palm Springs; Vancouver, Canada; and Puerto Vallarta and Cabo San Lucas in Mexico. The airline is also offering $69 one-way flights to Palm Springs.

Alaska also operates seven flights daily out of Oakland International Airport and Norman Y. Mineta San Jose International Airport. The airline began flying out of SFO in 1979. Tickets can be purchased at Alaskaair.com.